With Mammograms, Timing May Matter

Dec. 14, 2010 -- Women who have regular mammograms should consider paying attention to when they are scheduled. New research finds the timing of mammograms could affect the accuracy of results.

''Try to schedule it during the first week of your menstrual cycle," says researcher Diana Miglioretti, PhD, a senior investigator at Group Health Research Institute in Seattle, who led the study. "The first day of your menstrual cycle is the day you start to bleed."

But she adds: "I don't want women to stress too much over this, if they can't get in."

Her study does show, however, that timing of mammograms can make a difference for women who regularly get them. For some reason, the timing did not seem to have the same effect on accuracy in the women studied who were getting their first mammogram, Miglioretti tells WebMD.

Timing of Mammograms: Backstory

Previous studies have looked at the timing of mammograms, Miglioretti says. Some experts have found that accuracy might be better in the first half of the cycle.

Other research has shown that breast density may be lower during the first half of the cycle. "We know breast density strongly affects mammography performance," she says. If a woman has a lot of dense tissue, it's more difficult to find cancer.

Timing of Mammograms: Study Details

Miglioretti and her colleagues examined 387,218 mammograms from women aged 35 to 54 who got the screenings from 1996 through 2007. The data were retrieved from six National Cancer Institute-funded Breast Cancer Surveillance Consortium mammography registries.

The researchers took into account when the women had the mammograms and whether it was their first or not. They found that for women who had already had a screening mammogram in the past two years, the sensitivity -- the number of true positive findings -- was highest in those who had the mammograms the first week of their cycle. ''It was about 80% the first week," Miglioretti says.